This invention relates to the art of vehicles having pneumatic tires and, more particularly, to improvements in connection with systems and apparatus for selectively inflating, deflating and checking vehicle tire pressure.
It is of course well known to provide vehicles with onboard systems for achieving inflating and/or deflating of vehicle tires and/or the checking of the pressure of air in the vehicle tires. Such systems generally include a source of air under pressure and manually operable controls for selectively increasing or decreasing an existing tire pressure and/or checking to determine the magnitude of the existing tire pressure. The ability to selectively increase or decrease tire pressure is desirable in connection with optimizing operation of the vehicle under variable and changing conditions including, for example, weather, vehicle load, terrain and vehicle speed. It is likewise desirable in connection with such capability to provide for isolating the air under pressure in each vehicle tire from the remainder of the system so that a problem such as a leak encountered in connection with one tire does not affect the air pressure in the other vehicle tires. Further in connection with such a tire isolating feature, an air line or lines from the system's source of air under pressure extends to a vehicle tire generally through the fixed axle upon which the tire and its associated wheel assembly are rotatably mounted and across a sealing arrangement between the fixed and rotating parts, and the tire isolating valve is preferably between the sealing arrangement and tire so that the sealing arrangement is not subjected to system air under pressure other than at times of operation of the system to achieve inflation, deflation or pressure checking.
Problems encountered in connection with systems of the foregoing character heretofore available have included the inability to accurately obtain a predetermined desired tire pressure during inflation or deflation, the inability to achieve inflation or deflation from one tire pressure to another with accuracy and within a desired time period, and the inability to provide a system which is efficient in operation both from the standpoint of minimizing operator assistance and obtaining optimum inflating and deflating rates and accuracy with respect to the tire pressure sought. Accuracy in connection with obtaining a desired tire pressure has been difficult to achieve for a number of reasons including, for example, reliance on manually actuable controls for initiating and terminating an inflating or deflating process in connection with a visual observation of tire pressure during the process, and/or the use of flow control valves which are slow to close upon termination of the process whereby air under pressure from the tires is lost before the valves close. These factors require anticipation and guess work on the part of the operator in an effort to compensate for such air pressure loss and/or to terminate the inflating or deflating operation when the desired pressure is reached.
Efforts to improve accuracy with respect to obtaining a desired tire pressure have included the use of complex flow control valves and/or slow flow rates between the source of air under pressure and the vehicle tires. However, such efforts result in the inability to achieve tire inflating or deflation within a given time period and which time period may be a critical requirement in connection with acceptance of a tire inflating and deflating system. Moreover, complex flow control valves or valve arrangements are undesirably expensive both to manufacture and to maintain. Such slow inflating or deflating rates and/or requirements for operator attention and/or assistance in connection with controlling the inflating or deflating process result in a less than desirable efficiency in connection with use of the system as well as the inability to continuously achieve accurate pressures in connection with use of the system.